1. Check to ensure that all email addresses entered are correct.

2. Check your email settings to ensure that your email is sending out correctly.

3. If sending to a large group, make sure you are not sending too many emails at once to avoid the emails being considered spam.

4. Contact your email provider if you have any issues or cannot find settings that appear to be wrong.

5. Make sure that emails are not blocked by any filters, such as company firewalls or anti-spam filters.

6. Consider using an email delivery service to ensure successful delivery of your messages.